The invention is particularly well suited for use in building tires from rubber material reinforced with wire cords, especially in the calendering operation where the wire tire cords are embedded in the unvulcanized rubber material. Two masses of unvulcanized rubber material are drawn between the nips of two pairs of rollers to form the rubber material into two thin sheets for calendering the wire tire cords. Occasionally, air becomes trapped in the rubber material during this sheet-forming operation. The air bubbles, thus created, must be eliminated since they can cause misorientation of the wire cords during the calendering process. This can be accomplished by continually pricking the sheets of unvulcanized rubber material to allow the escapement of air. Pricker rolls are provided for this purpose and have been used in the past to place a pattern of small circular holes in the thin sheets of unvulcanized rubber material. This particular pattern of cuts, however, has not proved effective in eliminating entrapped air. The invention is directed to providing a highly improved pattern of slots or cuts in the thin rubber sheets used in calendering wire tire cords.
Briefly stated, the invention is in a calender for embedding tire cords in rubber material. The calender comprises at least one rotatable roll for pricking a pattern of configured openings in sheets of rubber material, prior to contact with the tire cords. The roll includes a plurality of teeth which extend in spaced relation from the roll for piercing the rubber material. Each tooth is designed for cutting an elongated slot having its longitudinal axis angularly disposed to the longitudinal axis of the cord reinforced material being formed, or the longitudinal axis of the parallel cords being embedded in the rubber material.